A turnbuckle is a piece of hardware used to eliminate slack and adjust tension in a rope, cable, or other tensioning system.
ASME B30.26 – Rigging Hardware defines a turnbuckle as “an adjustable device consisting of three primary components: a body, a right-hand threaded end fitting, and a left-hand threaded end fitting.”
The end fitting on either side of a turnbuckle connects to the tensioning system and/or a securement point. The turnbuckle is then tightened or loosened to adjust tension and eliminate slack in the cable or rope is it connected to.
A turnbuckle may be used on its own or in conjunction with other turnbuckles to increase length in the assembly.
End Fittings: these are the two connection points that screw into the opposite ends of the turnbuckle body. One end fitting is right-hand threaded while the other is left-hand threaded. This allows you to turn the body to adjust tension after installation without moving the end fittings.
There are three main types of end fittings that can be used together in any combination on either end of the turnbuckle:
Hook end – a hook end fitting is used to create temporary connections because they are easy to quickly connect and disconnect. They should never be used in connections where tension could unexpectedly release.
Jaw end – a jaw end fitting consists of a jaw and bolt secured together by a nut or a pin. These are used to connect to components that cannot be opened, such as an eye bolt.
Eye end – an eye end fitting is a closed loop that can be connected to a shackle or quick link.
Thread diameter: this is the diameter measurement of the threaded portion of the end fittings. The greater the thread diameter is, the greater the load-bearing capacity of the turnbuckle and vice versa.
Take-up length: this is the total length that the end fittings can screw into and out of the body to “take up” tension. Take-up length can be measured in terms of “opened” or “closed” end fittings: the end fittings are either fully extended or fully retracted.
Types of Turnbuckles
Turnbuckle types are, essentially, named for the combination of end fittings used in the device. The most common end fitting combinations are:
Jaw and jaw
Eye and jaw
Eye and eye
Hook and hook
Hook and eye
Turnbuckle Inspection and Removal From Service Criteria
During the course of an inspection, remove the turnbuckle from service if any of the conditions listed in ASME B30.26 – Rigging Hardware are present:
Missing or illegible identification
Indications of heat damage, including weld spatter or arc strikes
Excessive pitting or corrosion
Bent, twisted, distorted, stretched, elongated, cracked, or broken load-bearing components
Excessive nicks or gouges
A 10% reduction of the original or catalog dimension at any point
Excessive thread damage or wear
Evidence of unauthorized welding or modification
Other conditions, including visible damage, that cause doubt as to continued use
